Bioreductively activated stilbene prodrugs

ABSTRACT

A compound of formula (1), or a pharmaceutically acceptable salt thereof, wherein Ar is a substituted heteroaryl group bearing at least one nitro or azido group or is a group of formula (2) or (3); R1 is hydrogen, optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl; R 2  is alkyl, alkoxy, thialkoxy or halo; R 3 , R 4  and R 5  are each independently alkyl, alkoxy, thialkoxy or halo with the proviso that at least two of R 3 , R 4  or R 5  are alkoxy; L is —OC(O)— or —OP(O)(OR 6 )—; n is 0 or 1; X is O, S or NR 7 ; Y is hydrogen, alkyl, alkoxy, thialkoxy, halo, hydroxy or dihydrogenphosphate; R 6  is hydrogen or alkyl; R 7  is hydrogen or alkyl; R 8  is hydrogen, alkoxy or dialkylaminoalkyl; R 9  is optionally substituted alkyl; R 10  is hydrogen, alkyl, alkoxy or dialkylaminoalkyl; R 11 , and R 12  are independently hydrogen, alkyl, alkoxy, thialkoxy, amono alkylamino, dialkylamino, morpholino, alkylmorpholino, piperidino, alkylpiperidiono, piperazino, alkylpiperazino or 1-aziridinyl; and A, together with the carbon atoms to which it is fused, is an optionally substituted aryl or heteroaryl ring.

This invention relates to compounds useful in the treatment of cellproliferation disorders. More particularly the invention relates to aseries of compounds that are activated under hypoxic conditions.

Many drugs used in conventional cancer chemotherapy are toxic to growingcancer cells but lack complete specificity. Thus other normal tissuesare affected and ensuing side effects limit the dose that can beadministered. Therefore the exposure of the cancerous tumour to thecompound, and in turn the effectiveness of the therapy, is limited.Recent research has shown promising clinical activity of compounds, suchas protein kinase inhibitors, which are cytostatic in their action.However the specificity of such compounds is not complete and sideeffects arising from action against normal tissues can again limit theeffectiveness of therapy. There is a need for drugs that target thetumour more selectively.

Many solid tumours exhibit regions of hypoxia (low oxygen tension).Inadequate blood supply to the central regions of the tumour results inhypoxia that can be chronic or acute. This hypoxia represents achallenge to effective therapy by radiation or by conventionalchemotherapy since hypoxic regions are often more resistant to thesemodalities. It has been suggested, however, that tumour hypoxia can beused to target tumours for drug action (Kennedy, Cancer Res. 1980, 40,2356-2360.). One particular method of using the hypoxic regions oftumours for drug targeting is the selective activation of produgs underconditions of low oxygen tension. A concept has been advanced wherebythe activity of a cytotoxic compound can be masked by a trigger moietywhich, under hypoxic conditions, mediates fragmentation of the maskedcytotoxic compound into the active cytotoxic agent (Denny, Lancet Oncol2000, 1, 25-9). Compounds attempting to utilize this concept typicallyconsist of the trigger moiety attached, often via a linker moiety, to acytotoxic moiety (the effector).

Hypoxia is also a feature of the rheumatoid arthritic joint (RothschildSemin Arthritis Rheum 1982, 12, 11-31). Cell proliferation is also afeature of the arthritic joint. Systemic antiproliferative drugs (forexample methotrexate) are used in the therapy of rheumatoid arthritisbut are limited by side effects. Psoriatic lesions are alsocharacterized by cell proliferation and hypoxia (Dvorak Int Arch AllergyImmunol. 1995, 107, 233-5. Hypoxia drives proliferation of endothelialcells in the retina in diabetic retinopathy and in the choroid of theeye in wet age-related macular degeneration (Das, Prog Retin Eye Res2003, 22, 721-48).

A number of hypoxic trigger moieties have been disclosed includingnitrobenzenes, nitronaphthalenes, nitroimidazoles, nitrofurans,nitrothiophenes, nitropyrroles, nitropyrazoles, benzoquinones,naphthoquinones, indoloquinones and azidobenzenes (for some examples seeNaylor, Mini Rev. Med. Chem. 2001 1, 17-29; Tercel, J. Med. Chem. 2001,44, 3511-3522 and Damen, Bioorg. Med. Chem. 2002, 10, 71-77).

A number of effector moieties have been utilised in the art includingnitrogen mustards, phosphoramide mustards, taxanes, enediynes and indolederivatives (for some examples see Naylor, loc cit and Papot, Curr. Med.Chem. Anti Cancer Agents 2002, 2, 155-185).

Hypoxic triggers joined to effectors via a linking group have beendescribed wherein the linking group consists of a carbonate or carbamatefor some examples see Naylor, loc cit and Papot loc cit). In these casesit is intended that the intermediate carbonic acid or carbamic acid,formed by the initial hypoxia-driven fragmentation, further fragments togive the active agent.

The combretastatins are a series of stilbene compounds that havepowerful antiproliferative activity against cancer cell lines in vitro.Examples of such compounds include combretastatin A4 (U.S. Pat. No.4,996,237) and combretastatins A1 and A3 (U.S. Pat. No. 5,569,786).Cushman (U.S. Pat. No. 5,430,062) has disclosed a series of Z-stilbenesthat are related to the combretastatins and that have anticanceractivity. Davis (WO 01 12579) has also disclosed novel stilbenes relatedto the combretastatins as has Hadfield (WO 02 050007). Stilbeneanalogues containing an amino group have also been disclosed (U.S. Pat.No. 5,731,353).

It is thought that this antiproliferative activity of these Z-stilbenesis due to an antimitotic action brought about by the inhibition oftubulin polymerisation (see for example Woods et al. Br J Cancer 71,705-711, 1995). This antimitotic activity requires prolonged exposure ofthe cells to the compounds. Some of these compounds also have activityagainst tumour vasculature in vivo, which is distinct from theantimitotic activity observed in vitro. It is thought that theantimitotic activity of these compounds is generally not expressed invivo because, unlike the antivascular activity, a prolonged exposure ofthe tumour to the compounds is required and the short eliminationhalf-lives of the compounds preclude this exposure at non-toxic doses.Combretastatin analogues delivered to the tumour by a hypoxia-drivenfragmentation strategy offer the potential to deliver prolonged tumourexposure that may be antimitotic while minimising host toxicity. Thesecompounds could also result in generation of active combretastatincompounds at the site of inflammation in rheumatoid arthritis andpsoriasis, reducing the cell proliferation that is characteristic ofthese diseases. Such compounds could also reduce the proliferation ofendothelial cells in the retina or choroid associated with diseases suchas diabetic retinopathy and wet age-related macular degeneration.

It is an object of this invention to provide prodrugs that onbioreductive activation break down to release an antimitotic stilbenecompound.

Thus according to one aspect of the invention we provide a compound offormula (1), or a pharmaceutically acceptable salt thereof:

wherein:

-   -   Ar is a substituted heteroaryl group bearing at least one nitro        or azido group or is a group of formula (2) or (3);    -   R₁ is hydrogen, optionally substituted alkyl, optionally        substituted aryl or optionally substituted heteroaryl;    -   R₂ is alkyl, alkoxy, thioalkoxy or halo;    -   R₃, R₄ and R₅ are each independently alkyl, alkoxy, thioalkoxy        or halo with—the proviso that at least two of R₃, R₄ or R₅ are        alkoxy;    -   L is —OC(O)— or —OP(O)(OR₆)—;    -   n is 0 or 1;    -   X is O, S or NR₇;    -   Y is hydrogen, alkyl, alkoxy, thioalkoxy, halo, hydroxy or        dihydrogenphosphate;    -   R₆ is hydrogen or alkyl;    -   R₇ is hydrogen or alkyl;    -   R₈ is hydrogen, alkoxy or dialkylaminoalkyl;    -   R₉ is optionally substituted alkyl;    -   R₁₀ is hydrogen, alkyl, alkoxy or dialkylaminoalkyl;    -   R₁₁ and R₁₂ are independently hydrogen, alkyl, alkoxy,        thioalkoxy, amino, alkylamino, dialkylamino, morpholino,        alkylmorpholino, piperidino, alkylpiperidino, piperazino,        alkylpiperazino or 1-aziridinyl; and    -   A, together with the carbon atoms to which it is fused, is an        optionally substituted aryl or heteroaryl ring.

As used herein the term “alkyl”, alone or in combinations, means astraight or branched-chain alkyl group containing from one to seven,preferably a maximum of four, carbon atoms such as methyl, ethyl,propyl, isopropyl, butyl, sec-butyl, t-butyl and pentyl. Typically,alkyl group or moiety is a linear or branched alkyl group or moietycontaining from 1 to 6 carbon atoms, such as a C₁-C₄ or C₁-C₂ alkylgroup or moiety.

As used herein, alkoxy is a said alkyl group, for example a C₁-C₄ orC₁-C₂ alkyl group, which is attached to an oxygen atom.

As used herein, a thioalkoxy group is a said alkyl group which isattached to a sulphur atom.

Optional substituents which may be present on alkyl groups include oneor more substituents selected from halogen, ammo, monoalkylamino,dialkylamino, hydroxy, alkoxy, alkylthio, alkylsulphonyl, aryl,heteroaryl, acylamino, alkoxycarbonylamino, alkanoyl, acyloxy, carboxy,sulphate or phosphate groups. A further example of an optionalsubstituent which may be present on alkyl groups is a heterocycloalkylgroup. Preferably, the substituents on an alkyl group are selected fromhalogen, amino, mono(C₁-C₄ alkyl)amino, di(C₁-C₄ alkyl)amino, hydroxy,C₁-C₄ alkoxy and C₁-C₄ alkylthio groups. Typically, alkyl groups areunsubstituted or substituted by one, two or three substitutents.Typically, said substituents which may be present on alkyl groups arethemselves unsubstituted. More preferably, an alkyl group isunsubstituted or substituted by 1, 2 or 3 halogen atoms.

The term “halogen” means fluorine, chlorine, bromine or iodine. As usedherein, the term “halo” refers to a fluoro, chloro, bromo or iodosubstituent. Halo is typically fluoro or chloro.

The term aryl means an unsubstituted phenyl group or a phenyl groupcarrying one or more, preferably one to three, substituents examples ofwhich are halogen, optionally substituted alkyl, hydroxy, nitro, azido,cyano, amino and alkoxy. Preferably, an aryl group is an unsubstitutedphenyl group or a phenyl group substituted with 1, 2 or 3 unsubstitutedsubstituents selected from halogen, C₁-C₆ alkyl, hydroxy, amino, C₁-C₄haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy. More preferably, an arylgroup is a phenyl group which is unsubstituted or substituted with 1, 2,or 3 unsubstituted substituents selected from halogen, C₁-C₂ alkyl,C₁-C₂ haloalkyl, C₁-C₂ alkoxy and C₁-C₂ haloalkoxy substituents.

As used herein, a haloalkyl or haloalkoxy group is a said alkyl oralkoxy group, substituted by one or more said halogen atoms. Typically,a haloalkyl or haloalkoxy group is substituted by 1, 2 or 3 said halogenatoms. Preferred haloalkyl and haloalkoxy groups include perhaloalkyland perhaloalkoxy groups such as —CZ₃ and —OCZ₃ wherein Z is saidhalogen atom, for example chlorine or fluorine. Particularly preferredhaloalkyl groups are —CF₃ and —CCl₃. Particularly preferred haloalkoxygroups are —OCF₃ and —OCCl₃.

The term heteroaryl is defined herein as a mono- or fused bi-cyclicaromatic group containing one to four heteroatoms selected in anycombination from N, S or O atoms. A heteroaryl group is typically a 5-to 10-membered ring, such as a 5- or 6-membered ring, containing atleast one heteroatom, for example 1, 2, or 3 heteroatoms chosen from N,S or O atoms. Examples of heteroaryl groups include pyridyl, pyrimidyl,furyl, thienyl, pyrrolyl, pyrazolyl, indolyl, benzofuryl, benzothienyl,benzothiazolyl, oxazolyl, isoxazolyl, thiazolyl, isothiazolyl,imidazolyl, triazolyl, quinolyl and isoquinolyl groups. A heteroarylgroup can carry one or more, preferably one to three, substituentsexamples of which are halogen, optionally substituted alkyl, hydroxy,nitro, azido, cyano, amino and alkoxy. Preferably, a heteroaryl group isan unsubstituted hetoraryl group or a heteroaryl group substituted with1, 2 or 3 unsubstituted substituents selected from halogen, C₁-C₆ alkyl,hydroxy, amino, C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxysubstituents. More preferably, a heteroaryl group is unsubstituted orsubstituted with 1, 2, or 3 unsubstituted substituents selected fromhalogen, C₁-C₂ alkyl, C₁-C₂ haloalkyl, C₁-C₂ alkoxy and C₁-C₂ haloalkoxysubstituents.

A heterocycloalkyl ring is typically a non-aromatic, saturated orunsaturated C₃₋₁₀ carbocyclic ring in which one or more, for example, 1,2 or 3, of the carbon atoms are replaced by a heteroatom selected fromN, O or S. Saturated heterocycloalkyl groups are preferred. The termheterocycloalkyl ring includes heterocycloalkyl groups containing 3-6carbon atoms and one or two oxygen, sulphur or nitrogen atoms.Particular examples of such groups include azetidinyl, pyrrolidinyl,piperidinyl, homopiperidinyl, piperazinyl, homopiperazinyl, morpholinylor thiomorpholinyl groups.

Substituents which may be present on a heterocycloalkyl ring include oneor more groups selected from optionally substituted alkyl, halogen, oxo,hydroxy, alkoxy, alkylthio, amino, alkylamino, dialkylamino, carboxy,alkoxycarbonyl, aminocarbonyl, alkylaminocarbonyl, dialkylaminocarbonyl,alkylsulphonyl, aminosulphonyl, acylamino, alkoxycarbonylamino,alkanoyl, acyloxy, sulphate, phosphate and alkylphosphate. Preferably, aheterocycloalkyl ring is an unsubstituted heterocycloalkyl group or aheterocycloalkyl group substituted with 1, 2 or 3 unsubstitutedsubstituents selected from halogen, C₁-C₆ alkyl, hydroxy, amino, C₁-C₄haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy. More preferably, aheterocycloalkyl ring is unsubstituted or substituted with 1, 2, or 3unsubstituted substituents selected from halogen, C₁-C₂ alkyl, C₁-C₂haloalkyl, C₁-C₂ alkoxy and C₁-C₂ haloalkoxy substituents.

Typically, in the compound of formula (1), R₁ is hydrogen, unsubstitutedC₁-C₆ alkyl, a phenyl group which is unsubstituted or substituted with1, 2 or 3 unsubstituted substituents selected from halogen, C₁-C₆ alkyl,hydroxy, amino, C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy or aheteroaryl group which is unsubstituted or substituted with 1, 2 or 3unsubstituted substituents selected from halogen, C₁-C₆ alkyl, hydroxy,amino, C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy substituents.

Preferably, in the compound of formula (1), R₁ is hydrogen,unsubstituted C₁-C₄ alkyl, a phenyl group which is unsubstituted orsubstituted with 1, 2 or 3 unsubstituted substituents selected fromhalogen, C₁-C₄ alkyl, hydroxy, amino, C₁-C₂ haloalkyl, C₁-C₂ alkoxy andC₁-C₂ haloalkoxy.

A particularly useful group of compounds are those of formula (1) inwhich R₁ is an alkyl group.

More preferably, in the compound of formula (1), R₁ is hydrogen orunsubstituted C₁-C₂ alkyl.

Typically, in the compound of formula (I), R₂ is unsubstituted C₁-C₆alkyl, unsubstituted C₁-C₄ alkoxy, unsubstituted thio(C₁-C₄ alkoxy) or ahalo group.

More typically, in the compound of formula (1), R₂ is unsubstitutedC₁-C₄ alkyl, unsubstituted C₁-C₂ alkoxy, or a chloro or fluoro group.

Preferably, in the compound of formula (1), R₂ is an unsubstituted C₁-C₂alkoxy group.

Typically, in the compound of formula (1), R₃, R₄ and R₅ are the same ordifferent and each represent unsubstituted C₁-C₆ alkyl, unsubstitutedC₁-C₄ alkoxy, unsubstituted thio(C₁-C₄ alkoxy) or a halo group providedthat at least two of R₃, R₄ and R₅ are alkoxy.

More typically, in the compound of formula (1), R₃, R₄ and R₅ are thesame or different and each represent unsubstituted C₁-C₆ alkyl,unsubstituted C₁-C₂ alkoxy, or a halo group provided that at least twoof R₃, R₄ and R₅ are alkoxy.

Preferably, in the compound of formula (1) R₃, R₄ and R₅ are the same ordifferent and each represent unsubstituted C₁-C₂ alkoxy.

Typically, in the compound of formula (1), X is O, S or NR₇, wherein R₇is hydrogen or unsubstituted C₁-C₆ alkyl, for example unsubstitutedC₁-C₄ alkyl.

More typically, in the compound of formula (1), X is O, S or NH.

Preferably, in the compound of formula (1), X is O.

Typically, in the compound of formula (1), n is 0.

Typically, in the compound of formula (1), L is —OC(O)— or —OP(O)(OR₆)—,wherein R₆ is hydrogen or unsubstituted C₁₋₆ alkyl. Typically, in thecompound of formula (1), R₆ is hydrogen or unsubstituted C₁₋₄ alkyl.

Preferably, in the compound of formula (1), L is —OC(O)—.

Typically, in the compound of formula (1), Y is selected from hydrogen,unsubstituted C₁-C₆ alkyl, unsubstituted C₁-C₄ alkoxy, unsubstitutedthio(C₁-C₄ alkoxy), halo, hydroxy or dihydrogenphosphate substituents.

More typically, in the compound of formula (1), Y is selected fromhydrogen, unsubstituted C₁-C₄ alkyl, unsubstituted C₁-C₂ alkoxy orhydroxy substituents.

Preferably, in the compound of formula (1), Y is hydrogen.

Typically, in the compound of formula (1), R₅ is a hydrogen,unsubstituted C₁-C₄ alkoxy or unsubstituted di(C₁-C₆ alkyl)amino(C₁-C₆alkyl) substituent. More typically, in the compound of formula (1), R₈is a hydrogen or unsubstituted C₁-C₂ alkoxy substituent.

Typically, in the compound of formula (1), A is a phenyl group or a 5 or6 membered heteroaryl ring. Typically, the phenyl group or heteroarylring is unsubstituted or substituted with 1, 2 or 3 unsubstitutedsubstituents selected from halogen, C₁-C₄ alkyl, hydroxy, amino, C₁-C₄haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy substituents. Preferably,the phenyl group or heteroaryl ring is unsubstituted or substituted with1 or 2 unsubstituted substituents selected from halogen, C₁-C₂ alkyl andC₁-C₂ haloalkyl substituents.

Typically, in the compound of formula (1), Ar is a substituted aryl or5- to 10-membered heteroaryl group bearing at least one nitro or azidogroup or a group of formula (3).

Typically, when Ar is a substituted aryl or 5- to 10-membered heteroarylgroup bearing at least one nitro or azido group, it carries onesubstituent selected from a nitro or azido group and 0, 1 or 2 furtherunsubstituted substituents chosen from halogen, C₁-C₆ alkyl, hydroxy,amino, C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy substituents.Preferably, said further substituents are chosen from halogen,unsubstituted C₁-C₄ alkyl, hydroxy and amino substituents. Morepreferably, said substituents are unsubstituted C₁-C₂ alkylsubstituents. Typically, when Ar is a substituted aryl or 5- to10-membered heteroaryl group bearing at least one nitro or azido group,it is a phenyl or a 5- to 6-membered heteroaryl group carrying onesubstituent selected from a nitro or azido group, and 0, 1 or 2 saidfurther substituents More preferably, when Ar is a substituted aryl or5- to 10-membered heteroaryl group bearing at least one nitro or azidosubstituent, said group carries only one substituent which substituentis chosen from a nitro or azido group. Preferably, said substituent is anitro group.

More typically, when Ar is a substituted aryl or 5- to 10-memberedheteroaryl group bearing at least one nitro or azido group, Ar is phenylor a 5- or 6-membered heteroaryl group, for example a furanyl,imidazolyl or thienyl group, substituted by only one substituent whichsubstituent is a nitro substituent. Particularly useful values of themoiety Ar include nitroimidazole groups, for example2-nitroimidazol-5-yl and nitrothiophene groups, for example5-nitrothien-2-yl. Further particularly useful examples of the moiety Arinclude nitrofuranyl groups, for example 5-nitrofuran-2-yl.

Typically, when Ar is a group of formula (3), R₉ is an unsubstitutedC₁-C₆ alkyl group. More typically, R₉ is unsubstituted C₁-C₄ alkylgroup. Preferably, R₉ is an unsubstituted C₁-C₂ alkyl group.

Typically, when Ar is a group of formula (3), R₁₀ is selected fromhydrogen, unsubstituted C₁-C₆ alkyl, unsubstituted C₁-C₄ alkoxy orunsubstituted di(C₁-C₆ alkyl)amino(C₁-C₆ alkyl) substituents. Moretypically, R₁₀ is selected from hydrogen, unsubstituted C₁-C₄ alkyl orunsubstituted C₁-C₂ alkoxy substituents. Preferably, R₁₀ is anunsubstituted C₁-C₂ alkyl group.

Typically, when Ar is a group of formula (3), R₁₁ and R₁₂ are the sameor different and each represent a unsubstituted substituent selectedfrom hydrogen, C₁-C₆ alkyl, C₁-C₄ alkoxy, thio(C₁-C₄ alkoxy), amino,(C₁-C₆ alkyl)amino, di(C₁-C₆ alkyl)amino, morpholino, (C₁-C₆alkyl)morpholino, piperidino, (C₁-C₆ alkyl)piperidino, piperazino,(C₁-C₆ alkyl)piperazino and 1-aziridinyl substituents. More typically,R₁₁ and R₁₂ are the same or different and each represent anunsubstituted substituent selected from hydrogen, C₁-C₄ alkyl, C₁-C₂alkoxy, thio(C₁-C₂ alkoxy) and (C₁-C₄ alkyl)piperidino substituents.Preferably, R₁₁ and R₁₂ are the same or different and each represent asubstituent selected from hydrogen, unsubstituted C₁-C₂ alkoxy andunsubstituted (C₁-C₂ alkyl)piperidino substituents.

In the compound of formula (1), preferably R₂, R₃, R₄ and R₅ are thesame and represent unsubstituted methoxy. It is further preferred that,in the compound of formula (1), R₂, R₃, R₄ and R₅ are the same andrepresent unsubstituted methoxy and Y represents hydrogen.

Preferably, in the compound of formula (1),

-   -   R₁ is hydrogen, unsubstituted C₁-C₆ alkyl, a phenyl group which        is unsubstituted or substituted with 1, 2 or 3 unsubstituted        substituents selected from halogen, C₁-C₆ alkyl, hydroxy, amino,        C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy or a        heteroaryl group which is unsubstituted or substituted with 1, 2        or 3 unsubstituted substituents selected from halogen, C₁-C₆        alkyl, hydroxy, amino, C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄        haloalkoxy;    -   R₂ is unsubstituted C₁-C₆ alkyl, unsubstituted C₁-C₄ alkoxy,        unsubstituted thio(C₁-C₄ alkoxy) or a halo group;    -   R₃, R₄ and R₅ are the same or different and each represent        unsubstituted C₁-C₆ alkyl, unsubstituted C₁-C₄ alkoxy,        unsubstituted thio(C₁-C₄ alkoxy) or a halo group provided that        at least two of R₃, R₄ and R₅ are alkoxy;    -   n is 0 or 1, wherein when n is 1, L is —OC(O)— or —OP(O)(OR₆)—;    -   R₆ is hydrogen or unsubstituted C₁₋₆ alkyl;    -   X is O, S or NR₇;    -   R₇ is hydrogen or unsubstituted C₁-C₆ alkyl;    -   Y is selected from hydrogen, unsubstituted C₁-C₄ alkyl,        unsubstituted C₁-C₂ alkoxy or hydroxy substituents; and    -   Ar is either (a) a substituted aryl or 5 to 10 membered        heteroaryl group which carries one substituent selected from a        nitro or azido group and 0, 1 or 2 further unsubstituted        substituents chosen from halogen, C₁-C₆ alkyl, hydroxy, amino,        C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy substituents;        or (b) a group of formula (3), wherein:        -   R₉ is an unsubstituted C₁-C₆ alkyl group;        -   R₁₀ is selected from hydrogen, unsubstituted C₁-C₆ alkyl,            unsubstituted C₁-C₄ alkoxy or unsubstituted di(C₁-C₆            alkyl)amino(C₁-C₆alkyl) substituents; and        -   R₁₁ and R₁₂ are the same or different and each represent an            unsubstituted substituent selected from hydrogen, C₁-C₆            alkyl, C₁-C₄ alkoxy, thio(C₁-C₄ alkoxy), amino, (C₁-C₆            alkyl)amino, di(C₁-C₆ alkyl)amino, morpholino, (C₁-C₆            alkyl)morpholino, piperidino, (C₁-C₆ alkyl)piperidino,            piperazino, (C₁-C₆ alkyl)piperazino and 1-aziridinyl            substituents.            More preferably, in the compound of formula (1),    -   R₁ is hydrogen or unsubstituted C₁-C₂ alkyl;    -   R₂ is an unsubstituted C₁-C₂ alkoxy group;    -   R₃, R₄ and R₅ are the same or different and each represent        unsubstituted C₁-C₂ alkoxy;    -   n is 0 or 1, wherein when n is 1, L is —OC(O)—;    -   X is O;    -   Y is hydrogen; and    -   Ar is either (a) 2-nitroimidazol-5-yl, 5-nitrothien-2-yl or        5-nitrofuran-2-yl; or (b) a group of formula (3), wherein:        -   R₉ is an unsubstituted C₁-C₂ alkyl group;        -   R₁₀ is an unsubstituted C₁-C₂ alkyl group; and        -   R₁₁ and R₁₂ are the same or different and each represent a            substituent selected from hydrogen, unsubstituted C₁-C₂            alkoxy and unsubstituted (C₁-C₂ alkyl)piperidino            substituents.

More preferably, the compound of formula (1) is selected from1-(4-Methoxy-3-(5-nitrothien-2-yl)methoxy)phenyl-2-(3,4,5-trimethoxy)phenyl-Z-ethene,1-(4-Methoxy-3-(1-(5-nitrothien-2-yl)ethoxy))phenyl-2-(3,4,5-trimethoxy)phenyl-Zethene,1-(4-Methoxy-3-(5-nitrothien-2-yl)methoxycarbonyloxy)phenyl-2-(3,4,5-trimethoxy)phenyl-Z-ethene,5-Methoxy-3-((3,4,4′,5-tetramethoxy-(Z)-stilbene-3′-yl)oxy)methyl-1,2-dimethylindole-4,7-dioneand3-((3,4,4′,5-Tetramethoxy-(Z)-stilbene-3′-yl)oxy)methyl-1,2-dimethyl-5-(4-methylpiperazin-1-yl)indole-4,7-dione.

Where one or more functional groups in compounds of formula (1) aresufficiently basic or acidic the formation of salts is possible.Suitable salts include pharmaceutically acceptable salts for exampleacid addition salts including hydrochlorides, hrdrobromides, phosphates,sulphates, hydrogen sulphates, alkylsulphonates, arylsulphonates,acetates, benzoates, citrates, maleates, fumarates, succinates, lactatesand tartrates, salts derived from inorganic bases including alkali metalsalts such as sodium or potassium salts, alkaline earth metal salts suchas magnesium or calcium salts, and salts derived from organic aminessuch as morpholine, piperidine or dimethylamine salts.

Those skilled in the art will recognise that compounds of formula (1)may exist as stereoisomers and/or geometrical isomers and accordinglythe present invention includes all such isomers which have anticanceractivity and mixtures thereof.

It is a further object of this invention to provide methods for thepreparation of compounds of Formula (1).

Compounds of Formula (1) may be prepared by a number of processes asgenerally described below and more specifically in the Exampleshereinafter. In the following process description, the symbols Ar, R₁and R₂ when used in the formulae depicted are to be understood torepresent those groups described above in relation to Formula (1) unlessotherwise indicated. In the schemes described below it may be necessaryto employ protecting groups that are then removed during the finalstages of the synthesis. The appropriate use of such protecting groupsand processes for their removal will be readily apparent to thoseskilled in the art.

Compounds of Formula (1) in which X is O or S and n is 0 can be preparedby Mitsunobu reaction of an alcohol of formula (4) with a stilbene offormula (5) in a solvent such as an ether solvent, for exampletetrahydrofuran, diethyl ether or dioxan or in a solvent such as anaromatic hydrocarbon for example benzene or toluene or in a solvent suchas an aprotic solvent for example dimethylformamide, in the presence ofa phosphine for example triphenylphosphine or tri-n-butylphosphine andin the presence of an azo compound such as diethylazodicarboxylate,diisopropylazodicarboxylate or 1,1′-(azodicarbonyl)dipiperidine at atemperature from about 0° C. to about the reflux temperature of thesolvent, conveniently at room temperature.

Alcohols of formula (4) are either known or can be prepared by standardmethods apparent to one skilled in the art. Such methods includetreatment of an aldehyde or ketone of formula (6) with a reducing agent,for example a borohydride reducing agent such as sodium borohydride in asolvent such as an alcoholic solvent for example methanol at atemperature between about −20° C. to room temperature, preferably around0° C. Such methods also include the treatment of an aldehyde of formula(7) with an organometallic compound of formula (8) in which M representsa metal, metal halide or dialkylmetal, for example, Li, ZnBr, Mglr orMgI or dialkylaluminium in a solvent such as an ether solvent, forexample tetrahydrofuran or diethyl ether or in an aromatic solvent forexample benzene or toluene at a temperature of between about −78° C. toabout the reflux temperature of the solvent, preferably from about 0° C.to room temperature. Where Ar is a substituted aryl or heteroaryl groupbearing at least one nitro group such methods also include the aromaticelectrophilic nitration of the appropriate aryl substrate with anappropriate nitrating agent at a temperature of between about −78° C.and room temperature. Appropriate nitrating agents are, for example,nitric acid in a solvent such as an acid anhydride for example aceticanhydride or in a solvent such as an acid for example sulphuric acid oracetic acid; nitronium tetrafluoroborate in a solvent such as an ethersolvent, for example tetrahydrofuran or diethyl ether or in a solventsuch as acetonitrile or glacial acetic acid or in a solvent such as achlorinated solvent for example dichloromethane or dinitrogen tetroxidein a solvent such as an ether solvent, for example tetrahydrofuran ordiethyl ether or in a solvent such as acetonitrile or glacial aceticacid or in a solvent such as a chlorinated solvent for exampledichloromethane or in an aromatic solvent for example benzene ortoluene.

Compounds of formula (1) in which n=0 can also be prepared by treatmentof a halide of formula (9), in which Hal represents a chlorine, bromineor iodine atom, with a compound of formula (5), in a solvent such as anaprotic solvent such as dimethylformamide or in an ether solvent such asdiethyl ether or tetrahydrofuran, or in a ketone solvent such as acetonein the presence of a base such as a metal carbonate for examplepotassium carbonate or silver(I)carbonate or a base such as a metalhydride for example sodium hydride or potassium hydride, at atemperature of between about −78° C. to about the reflux temperature ofthe solvent preferably between 0° and room temperature.

Halides of formula (9) are either known or can be prepared by standardmethods apparent to one skilled in the art. Such methods include thehalogenation of a compound of formula (10) with a halogenating agentsuch as N-bromosuccinimide, N-chlorosuccinimide or bromine in a solventsuch as a chlorinated solvent for example dichloromethane or carbontetrachloride at a temperature of about between about 0° C. and thereflux temperature of the solvent.

Compounds of Formula (1) in which X is O, n is 1 and L is —OC(O)— can beprepared by treatment of an alcohol of formula (4) with an acid chlorideof formula (11) in a solvent such as a chlorinated solvent for exampledichloromethane or trichloromethane at a temperature of between about 0°C. and the reflux temperature of the solvent conveniently in thepresence of a base such as, for example, an amine base for examplepyridine or triethylamine.

Acid chlorides of formula (11) are either known or can be prepared bystandard methods apparent to one skilled in the art. Such methodsinclude treatment of a compound of formula (5) in which X═O withphosgene or triphosgene in a solvent such as a chlorinated solvent forexample dichloromethane or trichloromethane with or without the additionof dimethylformamide at a temperature of around 0° C. to roomtemperature.

Compounds of Formula (1) in which X is NH, n is 1 and L is —OC(O)— canbe prepared by treatment of an alcohol of formula (4) with an isocyanateof formula (12) in a solvent such as a chlorinated solvent for exampledichloromethane or trichloromethane at a temperature of between about 0°C. and the reflux temperature of the solvent conveniently in thepresence of a base such as, for example, an amine base for examplepyridine or triethylamine.

Compounds of formula (1) in which X is NR₇, n is 1 and L is —OC(O)— canbe prepared by treatment of a chloroformate of formula 13 with acompound of the formula (5) in which X═NR₇ in a solvent such as achlorinated solvent for example dichloromethane or trichloromethane at atemperature of between about 0° C. and the reflux temperature of thesolvent conveniently in the presence of a base such as, for example, anamine base for example pyridine or triethylamine.

Compounds of formula (1) in which n is 1 and L is —OP(O)(OR₆)— can beprepared by treatment of an alcohol of formula (4) with a compound ofthe formula (14) in a solvent such as a chlorinated solvent for exampledichloromethane or trichloromethane at a temperature of between about 0°C. and the reflux temperature of the solvent conveniently in thepresence of a base such as, for example, an amine base for examplepyridine or triethylamine.

Compounds of formula (1), wherein n is 1, L is —OC(O)— and X is S can,of course be made by the reaction of an appropriate acid chloride offormula Ar—CHR₁—O—C(O)Cl with a thiol having the formula (15), in asolvent such as a chlorinated solvent for example dichloromethane ortrichloromethane at a temperature of between about 0° C. and the refluxtemperature of the solvent conveniently in the presence of a base suchas, for example, an amine base for example pyridine or triethylamine.

Compounds of formula (1) can also be synthesized from other compounds offormula (1) by the application of standard methods, includingsubstitution reactions, functional group transformations, bond-formingreactions and cyclisations known in the art.

The starting materials for the above described schemes are commerciallyavailable or can be synthesized using standard techniques.

Preparation of a compound of Formula (1) as a single enantiomer or,where appropriate, diastereomer may be effected by synthesis from anenantiomerically pure starting material or intermediate or by resolutionof the final product in a conventional manner.

The compounds of the invention may be administered as a sole therapy orin combination with other treatments. For the treatment of solid tumourscompounds of the invention may be administered in combination withradiotherapy or in combination with other anti-tumour substances forexample those selected from mitotic inhibitors, for example vinblastine,vincristine, vinorelbine, paclitaxel and docetaxel; alkylating agents,for example cisplatin, carboplatin, oxaliplatin, nitrogen mustard,melphalan, chlorambucil, busulphan and cyclophosphamide;antimetabolites, for example 5-fluorouracil, cytosine arabinoside,gemcitabine, capecitabine, methotrexate and hydroxyurea; intercalatingagents for example adriamycin and bleomycin; enzymes, for exampleaspariginase; topoisomerase inhibitors for example etoposide,teniposide, topotecan and irinotecan; thymidylate synthase inhibitorsfor example raltitrexed; biological response modifiers for exampleinterferon; antibodies for example edrecolomab and trastuzumab; receptortyrosine kinase inhibitors for example gefitinib and erlotinib; andanti-hormones for example tamoxifen. Further examples of antibodieswhich can be administered in combination with the compounds of theinvention include, for example bevacizumab and cetuximab. A furtherexample of a receptor tyrosine kinase inhibitor which can beadministered in combination with the compounds of the invention isimatinib. Such combination treatment may involve simultaneous orsequential application of the individual components of the treatment.

For the prophylaxis and treatment of disease the compounds according tothe invention may be administered as pharmaceutical compositionsselected with regard to the intended route of administration andstandard pharmaceutical practice. Such pharmaceutical compositions maytake a form suitable for oral, buccal, nasal, topical, rectal orparenteral administration and may be prepared in a conventional mannerusing conventional excipients. For example for oral administration thepharmaceutical compositions may take the form of tablets or capsules.The compositions for oral administration may also be in the form oflozenges, aqueous or oily suspensions, dispersible powders or granules.For nasal administration or administration by inhalation the compoundsmay be conveniently delivered as a powder or in solution. Topicaladministration may be as an ointment or cream and rectal administrationmay be as a suppository. For parenteral injection (includingintravenous, subcutaneous, intramuscular, intravascular or infusion) thecomposition may take the form of, for example, a sterile solution,suspension or emulsion. The compounds of the invention may also beadministered as suppositories.

The dose of a compound of the invention required for the prophylaxis ortreatment of a particular condition will vary depending on the compoundchosen, the route of administration, the form and severity of thecondition and whether the compound is to be administered alone or incombination with another drug. Thus the precise dose will be determinedby the administering physician but in general daily dosages may be inthe range 0.001 to 100 mg/kg preferably 0.1 to 10 mg/kg.

Typically, daily dosage levels are from 0.05 mg to 2 g, for example from5 mg to 1 g.

The present invention therefore provides a pharmaceutical compositioncomprising a compound of formula (1), or a pharmaceutically acceptablesalt thereof, and a pharmaceutically acceptable carrier or diluent.

A further feature of the present invention is a compound of formula (1),or a pharmaceutically acceptable salt or solvate thereof, for use as amedicament. In particular, the present invention provides a compound offormula (1), or a pharmaceutically acceptable salt thereof, for thetreatment of the human or animal body.

The compounds of the present invention are therapeutically useful intreating, preventing, ameliorating or reducing incidence of aproliferative disorder. Typically, the proliferative disorder is ahypoxic disorder. A hypoxic disorder is typically a disorder in whichdiseased cells are present in a hypoxic environment. Examples of thedisorders that can be treated, prevented, ameliorated or disorders whoseincidence can be reduced, include cancer, rheumatoid arthritis,psoriatic lesions, diabetic retinopathy or wet age-related maculardegeneration.

Typically, the disorder is cancer. Preferably the cancer is a hypoxiccancer. A hypoxic cancer is, of course, a cancer wherein cancerous cellsare in a hypoxic environment. Most preferably, the cancer is a solidtumour or leukaemia. Typically the leukaemia is leukaemia involving thespleen or bone marrow.

According to a further aspect of the invention there is provided the useof a compound of formula (1), or a pharmaceutically acceptable salt orsolvate thereof, in the manufacture of a medicament for use in thetherapy of a warm-blooded animal, for example a human, suffering from aproliferative disease for example cancer. In particular, the presentinvention provides the use of a compound of formula (1), or apharmaceutically acceptable salt thereof, in the manufacture of amedicament for use in the treatment of the human or animal body, for theprevention or treatment of a said proliferative disorder.

According to a further aspect of the invention there is provided acompound of formula (1), or a pharmaceutically acceptable salt orsolvate thereof, for use in a method of treatment of the human or animalbody by therapy. In particular, the present invention provides a methodof ameliorating or reducing the incidence of a said proliferativedisorder in a patient, which method comprises administering to saidpatient an effective amount of a compound of formula (1), or apharmaceutically acceptable salt thereof.

A number of enzymes are capable of reducing aryl and heteroaryl nitrogroups. Strategies that increase the activity of such enzymes withinsolid tumours can therefore increase further the activity of prodrugsdependent on nitro reduction. Similarly a number of enzymes are capableof reducing quinones and indoloquinones and therefore similar strategiesare possible to increase the effectiveness of drugs requiring activationby quinone reduction. Such strategies include linking such enzymes to atumour-targeting antibody, administering such enzyme antibody conjugatesto a host with a solid tumour then, after the conjugate has localised tothe tumour, administering the prodrug. This approach is known asAntibody Directed Enzyme Prodrug Tharapy (ADEPT). Alternatively the geneencoding for the enzyme might be delivered selectively and/or expressedselectively, in the tumour before administration of the prodrug. Thisapproach is known as Gene Directed Enzyme Prodrug Therapy (GDEPT). Whenthe gene is delivered by a viral vector the approach is sometimes knownas Virus Directed Enzyme Prodrug Therapy (VDEPT).

Anlezark has disclosed nitroreductases and their use in an ADEPTstrategy. Prodrugs for use in this strategy were also disclosed (U.S.Pat. No. 5,633,158 and U.S. Pat. No. 5,977,065). In WO 00 047725Anlezark provides further disclosures of nitroreductase enzymes andtheir use in GDEPT strategies. Denny (WO 00 064864) has disclosednitroaryl and nitroheteroaryl prodrugs for use in a GDEPT strategy. Theuse of quinone-reducing enzymes in ADEPT, GDEPT and MDEPT (MacromoleculeDirected Enzyme Prodrug Therapy) is discussed in Skelly et al. Mini RevMed Chem. 2001, 1, 293-306.

Thus it is a further object of this invention to provide the use ofcompounds of formula (1) in combination with a reductase, anantibody-reductase conjugate, a macromolecule-reductase conjugate or DNAencoding a reductase gene, in a method of treatment for the human body.Thus, the present invention provides a method of ameliorating orreducing the incidence of a said proliferative disorder in a patient,which method comprises administering to said patient an effective amountof

-   (a) a compound of formula (1), or a pharmaceutically acceptable salt    thereof; and-   (b) a reductase, an anti-body reductase conjugate, a    macromolecule-reductase conjugate or DNA encoding a reductase gene.

Further, the present invention provides a product containing

-   (a) a compound of formula (1), or a pharmaceutically acceptable salt    thereof; and-   (b) a reductase, an anti-body reductase conjugate, a    macromolecule-reductase conjugate or DNA encoding a reductase gene    for simulataneous, separate or sequential use in the treatment of a    proliferative condition.

In a further aspect, the present invention provides a compound offormula (1′), or a pharmaceutically acceptable salt thereof:

wherein:

-   -   Ar is a substituted heteroaryl group bearing at least one nitro        or azido group or is a group of formula (2′) or (3′)    -   R₁ is hydrogen, optionally substituted alkyl, optionally        substituted alkenyl, optionally substituted alkynyl, aryl or        COR₆;    -   R₂ is alkyl, alkoxy, thioalkoxy or halo;    -   R₃, R₄ and R₅ are each independently alkyl, alkoxy, thioalkoxy        or halo with the proviso that at least two of R₃, R₄ or R₅ are        alkoxy;    -   L is —OC(O)— or —OP(O)(OR₇)—;    -   n is 0 or 1;    -   X is O, S or NR₈;    -   Y is hydrogen, alkyl, alkoxy, thioalkoxy, halo, hydroxy or        dihydrogenphosphate;    -   R₆ is OR₈ or NR₉R₁₀;    -   R₇, R₈, R₉ and R₁₀ are each independently hydrogen or alkyl;    -   R₁₁ is hydrogen, alkoxy or dialkylaminoalkyl;    -   R₁₂ is optionally substituted alkyl;    -   R₁₃ is hydrogen, alkyl, alkoxy or dialkylaminoalkyl;    -   R₁₄ and R₁₅ are independently hydrogen, alkyl, alkoxy,        thioalkoxy, amino, alkylamino, dialkylamino morpholino,        alkylmorpholino, piperidino, alkylpiperidino, piperazino,        alkylpiperazino or 1-aziridinyl; and    -   A is an optionally substituted aryl or heteroaryl ring.

In a compound of formula (1′), an alkenyl group may be for example anolefinic group containing from two to seven carbon atoms, for exampleethenyl, n-propenyl, i-propenyl, n-butyenyl, i-butenyl, s-butenyl andt-butenyl.

As used herein, in a compound of formula (1′), an alkynyl group may befor example an ethynyl, propynyl or butynyl group.

In a compound of formula (1′), optional substituents which may bepresent on alkenyl or alkynyl groups are the same as those which may bepresent on alkyl groups, as described above.

In the compound of formula (1′), particularly useful values of themoiety Ar include nitroimidazole groups, for example2-nitroimidazol-5-yl, and nitrothiophene groups, for example5-nitro-thiophen-2-yl.

Where one or more functional groups in compounds of formula (1′) aresufficiently basic or acidic the formation of salts is possible.Suitable salts include those as described above with respect to acompound of formula (1).

Those skilled in the art will recognise that compounds of formula (1′)may exist as stereoisomers and/or geometrical isomers and accordinglythe present invention includes all such isomers which have anticanceractivity and mixtures thereof.

The present invention therefore provides a pharmaceutical compositioncomprising a compound of formula (1′), or a pharmaceutically acceptablesalt thereof, and a pharmaceutically acceptable carrier or diluent.

A further feature of the present invention is a compound of formula(1′), or a pharmaceutically acceptable salt or solvate thereof, for useas a medicament. In particular, the present invention provides acompound of formula (1′), or a pharmaceutically acceptable salt thereof,for the treatment of the human or animal body.

According to a further aspect of the invention there is provided the useof a compound of formula (1′), or a pharmaceutically acceptable salt orsolvate thereof, in the manufacture of a medicament for use in thetherapy of a warm-blooded animal, for example a human, suffering from aproliferative disease for example cancer. In particular, the presentinvention provides the use of a compound of formula (1), or apharmaceutically acceptable salt thereof, in the manufacture of amedicament for use in the treatment of the human or animal body, for theprevention or treatment of a said proliferative disorder.

The ability of compounds of the invention to release cytotoxic orcytostatic agents selectively under hypoxic conditions can be assessedby using, for example, one or more of the procedures set out below:

Radiolysis

In the hypoxic environments of solid tumours, prodrugs can be reduced byone-electron processes that are inhibited in the normoxic environmentsof normal tissues.

Radiolysis demonstrates the ability of bioreductively-activated prodrugsto release the active drug after one-electron reduction. Compounds weredissolved in an isopropanol/water mixture (50:50) at a concentration of50 μM or below. Solutions, in gas-tight syringes, were saturated withnitrous oxide before irradiation in a ⁶⁰Co source at a dose rate of 3.9Gy min⁻¹ (as determined by Fricke dosimetry: H. Fricke and E. J. Hart,“Chemical Dosimetry” in Radiation Dosimetry Vol. 2 (F. H. Attrix and W.C. Roesch. Eds.), pp 167-239. Academic Press New York, 1966.). Solutionswere analysed for released drug by HPLC. The radiation chemical yields(G-values) of combretastatin A4 release obtained in this assay forselected example compounds are shown in Table 1. TABLE 1 Radiationchemical yields from steady state radiolysis Compound of Example No. G(μmoles · J⁻¹) 1 0.23 2 0.33 4 0.44 5 0.34Metabolism in Tumour HomogenatesUseful bioreductive prodrugs can be shown to release the active drugselectively under conditions of low oxygen in the presence of tumourhomogenate in this assay. Freshly-excised CANT tumours (approximately0.5 to 1 g) were homogenised in 15 ml of ice-cold 50 mmol dm 3 potassiumphosphate buffer at pH 7.4. The homogenates were centrifuged at 1000 RPMfor 10 min and the supernatants stored on ice. The metabolism of 5 μmoldm⁻³ prodrug in air and N₂ was performed with 0.5 ml tumour homogenate(˜3 mg of protein by Bradford assay) with 100 μmol dm⁻³ NADPH in 50 mmoldm⁻³ potassium phosphate buffer at pH 7.4 incubated at 37° C. Samples(60 μl) were taken at regular intervals and added to an equivalentvolume of acetonitrile, then mixed and centrifuged at 14, 300 RPM for 2min prior to product analysis by HPLC. In this test the compound ofExample 1 produced combretastatin A4 at a rate of 310 pmol. min⁻¹ .mgprotein⁻¹ under nitrogen but only 30 nmol. min⁻¹ .mg protein⁻¹ underair.Cellular CytotoxicityThe cytotoxic or cytostatic properties of compounds of formula (1) andcompounds of formula DrXH can be assessed for example, by use, forexample, of this assay. The Celltiter 96® Aq_(ueous) One Solution CellProliferation Assay kit (Promega Corporation, USA) which is acalorimetric method for determining the number of viable cells inproliferation or cytotoxicity assays was used. In this assay the MTStetrazolium compound (Owen's Reagent) is bioreduced by viable cells intoa coloured formazan product which is soluble in tissue culture mediumand can be measured by recording absorbance at 490 nm with a 96 wellplate reader. A549 cells were seeded in Eagles Minimum Essential Mediumsupplemented with 10% foetal calf serum and non-essential amino acids at10³ cell per well on a 96 well plate and allowed to attach for 24 h.Compounds were dissolved in DMSO and diluted with cell culture mediumbefore addition to The cells were exposed to test compound (0 to 2 μmoldm⁻³) for 6 h then incubated for a further 72 h. The MTS reagent wasadded to each well, left for 4 h, then the absorbance measured at 490 nmwith a 96 well plate reader.

The invention is illustrated by the following non-limiting Examples inwhich, unless otherwise stated:DMF means dimethylformamideTHF means tetrahydrofuranMeOH means methyl alcoholEtOAc means ethyl acetateDCM means dichloromethaneTLC means thin-layer chromatographyTFA means trifluoroacetic acidMeCN means acetonitrileLC-RT means the retention time given by high-performance liquidchromatography performed using a Waters Integrity system with detectionby mass spectroscopy with electron impact ionization. Chromatographyused a Hichrom RPB column (100×3.2 mm) with various solvent gradients ofeither A: 10% acetonitrile, water or B: 5% Acetonitrile, 0.1% TFA withC: Acetonitrile, at a flow rate of 0.5 ml/min.

EXAMPLE 11-(4-Methoxy-3-(5-nitrothien-2-yl)methoxy)phenyl-2-(3,4,5-trimethoxy)phenyl-Z-ethene

5-Nitro-2-hydroxymethylthiophene (500 mg, 3.14 mmol) was dissolved inTHF (5 ml) together with triphenylphosphine (1.68 g, 6.28 mmol) andcombretastatin A4 (1.98 g, 6.28 mmol). To this solution was addeddiethylazodicarboxylate (1.09 g, 6.28 mmol) and the solution heated at50° C. for 3 h, evaporated to dryness and the residue purified on silica(25% EtOAc/hexane) to give a pale yellow solid (mp 88-90° C., 810 mg,57%) after recrystallisation from EtOAc/hexane. LC-RT 9.98 minutes (TFA50-100%; MS (m/z, %) 457 (M+, 85%), 316 (61%), 301 (47%), 252 (100%).Anal. C, 60.5; H, 5.1, N, 2.9% C₂₃H₂₃NO₇S requires C, 60.4; H, 5.1, N,3.1%.

EXAMPLE 21-(4-Methoxy-3-(1-(5-nitrothien-2-yl)ethoxy))phenyl-2-(3,4,5-trimethoxy)phenyl-Z-ethene

Diethylazodicarboxylate (357 mg, 2.05 mmol) was added dropwise to asolution of alcohol 2-(1-hydroxyethyl)-5-nitrothiophene (55 mg, 0.32mmol), combretastatin A4 (648 mg, 2.05 mmol), triphenylphosphine (288mg, 1.10 mmol) and THF (3 mL). The reaction was stirred for 16 hours atambient temperature and was then partitioned (EtOAc, brine), aqueousphase extracted (EtOAc), organic phase washed (H₂O, brine), dried(NgSO₄) and concentrated in vacuo. Flash chromatography, elutingsequentially with 50% EtOAc/hexane then 100% EtOAc, furnished thedesired product as a yellow oil (15 mg, 10%). LC-RT 3.85 minutes (100%MeCN). MS (m/z, %) 471 (M⁺), 425 (M⁺—NO₂), 316, 301, 141.

EXAMPLE 31-(4-Methoxy-3-(5-nitrothien-2-yl)methoxycarbonyloxy)phenyl-2-(3,4,5trimethoxy)phenyl-Z-ethene

Phosgene (0.5 ml, 1 mmol) was dissolved in DCM (1 ml) at 0° C. and underan argon atmosphere. To this solution was added combretastatin A4 (100mg, 0.32 mmol) in DCM (0.5 ml) followed by triethylamine (60 μl, 0.4mmol) after 1 h at 0° C. The solution was then stirred for 18 h whilewarming to 20° C., and then evaporated to dryness and re-dissolved inDCM (1 ml). To this was added triethylamine (56 ml, 0.4 mmol) and5-nitro-2-hydroxymethylthiophene (60 mg, 0.376 mmol) and the solutionstirred at 20° C. for 5 days then evaporated to dryness. The residue waspurified on silica (hexane/EtOAc, 4:1) to give a residue that was thenpurified by preparative HPLC (CH₃CN/H₂O, 9:1) to give 10 mg (7.5%) of apale yellow gum. LC-RT 3.22 minutes (100% MeCN). MS (m/z, %) 501 (M+,100%), 316 (55%), 301 (46%), 252 (50%).

EXAMPLE 45-Methoxy-3-((3,4,4′,5-tetramethoxy-(Z)-stilbene-3′-yl)oxy)methyl-1,2-dimethylindole-4,7-dione

Thionyl chloride (0.78 g, 6.5 mmol) was added drop-wise with stirring toa solution of 3-hydroxymethyl-5-methoxy-1,2-dimethylindole-4,7-dione(0.03 g, 0.13 mmol) in DCM (2 mL). The solution was stirred at 20° C.for 1.5 h and evaporated to dryness. The residue was redissolved in DMF(1.5 mL) and potassium carbonate (0.054 g, 0.39 mmol) added, followed bycombretastatin A4 (0.123 g, 0.39 mmol). The solution was stirred at 20°C. for 18 h and EtOAc (50 mL) added. The solution was washed with water(25 ml), saturated sodium bicarbonate (25 ml) and brine (25 ml), dried(MgSO₄) and evaporated. The residue was purified by radialchromatography, eluting with EtOAc to give the title compound (15 mg,21%) as an orange waxy solid: mp 192-194° C.; LC-RT 5.13 minutes (80%MeCN). MS (m/z, %) 533 (M⁺, 3%), 316 (27%), 301 (24%), 218 (100%). ¹HNMR (60 MHz, CDCl₃) δ 7.02 (m, 2H), 6.79 (m, 2H), 6.44 (m, 3H), 5.57 (s,1H), 5.12 (s, 2H), 3.85 (s, 3H), 3.78 (s, 6H), 3.67 (s, 6H), 2.26 (s,3H) ppm. Anal. Fnd. C, 67.1; H, 5.9, N, 2.6% C₃₀H₃₁NO₈ requires C, 67.5;H, 5.9, N, 2.6%.

EXAMPLE 53-((3,4,4′,5-Tetramethoxy-(Z)-stilbene-3′-yl)oxy)methyl-1,2-dimethyl-5-(4methylpiperazin-1-yl)indole-4,7-dione

The compound from Example 4 (53 mg, 0.1 mmol) was dissolved in anhydrousDMF (1.5 mL) together with 4-methylpiperazine (0.4 mL, ca 4 mmol). Thesolution was stirred at room temperature for 48 h and then EtOAc (25 mL)added. The solution was washed with saturated sodium bicarbonate (25 mL)and brine (25 mL), dried (MgSO₄) and evaporated. The residue waspurified on silica gel, eluting with 50% MeOH/EtOAc to give the titlecompound (28 mg, 47%) as a dark red gum. LC-RT 4.45 minutes (TFA50-100%). MS (m/z, %) 601 (M+, 7%), 316 (26%), 301 (19%), 286 (100%); ¹HNMR (60 MHz, CDCl₃) δ 7.21 (s, 1H), 7.0 (m, 3H), 6.5 (s, 1H), 6.45 (d,J=5 Hz, 2H), 5.44 (s, 1H), 5.06 (s, 2H), 3.84 (s, 3H), 3.78 (s, 6H),3.68 (s, 6H), 3.41 (m, 4H), 2.54 (m, 4H), 2.34 (s, 3H), 2.23 (s, 3H)ppm. MS (m/z, %) 601 (M⁺, 5%), 316 (19%), 301 (17%), 286 (100%). Anal.Fnd. C, 60.6; H, 6.2, N, 6.1% C₃₄H₃₉N₃O₇.4H₂O requires C, 60.6; H, 7.0,N; 6.2%.

1. A compound of formula (1), or a pharmaceutically acceptable saltthereof:

wherein: Ar is a substituted heteroaryl group bearing at least one nitroor azido group or is a group of formula (2) or (3);

R₁ is hydrogen, optionally substituted alkyl, optionally substitutedaryl or optionally substituted heteroaryl; R₂ is alkyl, alkoxy,thioalkoxy or halo; R₃, R₄ and R₅ are each independently alkyl, alkoxy,thioalkoxy or halo with the proviso that at least two of R₃, R₄ or R₅are alkoxy; L is —OC(O)— or —OP(O)(OR)—; n is 0 or 1; X is O, S or NR₇;Y is hydrogen, alkyl, alkoxy, thioalkoxy, halo, hydroxy ordihydrogenphosphate; R₆ is H or alkyl; R₇ is H or alkyl; R₈ is hydrogen,alkoxy or dialkylaminoalkyl; R₉ is optionally substituted alkyl; R₁₀ ishydrogen, alkyl, alkoxy or dialkylaminoalkyl; R₁₁ and R₁₂ areindependently hydrogen, alkyl, alkoxy, thioalkoxy, amino, alkylamino,dialkylamino, morpholino, alkylmorpholino, piperidino, alkylpiperidino,piperazino, alkylpiperazino or 1-aziridinyl; and A, together with thecarbon atoms to which it is fused, is an optionally substituted aryl orheteroaryl ring.
 2. A compound according to claim 1, wherein the alkylgroups in the R₁₋₇ and R₉₋₁₂ substituents are unsubstituted orsubstituted with 1, 2 or 3 unsubstituted substituents chosen fromhalogen, amino, mono(C₁-C₄ alkyl)amino, di(C₁-C₄ alkyl)amino, hydroxy,C₁-C₄ alkoxy and C₁-C₄ alkylthio substituents.
 3. A compound accordingto claim 1, wherein the aryl and heteroaryl groups in the Ar, A and R₁substituents are unsubstituted or substituted with 1, 2 or 3unsubstituted substituents selected from halogen, C₁-C₆ alkyl, hydroxy,amino, C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy.
 4. A compoundaccording to claim 1, wherein R₁ is hydrogen, unsubstituted C₁-C₆ alkyl,a phenyl group which is unsubstituted or substituted with 1, 2 or 3unsubstituted substituents selected from halogen, C₁-C₆ alkyl, hydroxy,amino, C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy or aheteroaryl group which is unsubstituted or substituted with 1, 2 or 3unsubstituted substituents selected from halogen, C₁-C₆ alkyl, hydroxy,amino, C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄ haloalkoxy substituents.5. A compound according to claim 1, wherein R₁ is hydrogen orunsubstituted C₁-C₂ alkyl.
 6. A compound according to claim 1, whereinR₂ is unsubstituted C₁-C₆ alkyl, unsubstituted C₁-C₄ alkoxy,unsubstituted thio(C₁-C₄ alkoxy) or a halo group.
 7. A compoundaccording to claim 1, wherein R₂ is an unsubstituted C₁-C₂ alkoxy group.8. A compound according to claim 1, wherein R₃, R₄ and R₅ are the sameor different and each represent unsubstituted C₁-C₆ alkyl, unsubstitutedC₁-C₄ alkoxy, unsubstituted thio(C₁-C₄ alkoxy) or a halo group providedthat at least two of R₃, R₄ and R₅ are alkoxy.
 9. A compound accordingto claim 1, wherein R₃, R₄ and R₅ are the same or different and eachrepresent unsubstituted C₁-C₂ alkoxy.
 10. A compound according to claim1, wherein X is O, S or NR₇, wherein R₇ is hydrogen or unsubstitutedC₁-C₆ alkyl.
 11. A compound according to claim 1, wherein X is O, S orNH.
 12. A compound according to claim 1, wherein L is —OC(O)— or—OP(O)(OR₆)—, wherein R₆ is hydrogen or unsubstituted C₁₋₆ alkyl.
 13. Acompound according to claim 1, wherein L is —OC(O)—.
 14. A compoundaccording to claim 1, wherein n is
 0. 15. A compound according to claim1, wherein Y is selected from hydrogen, unsubstituted C₁-C₆ alkyl,unsubstituted C₁-C₄ alkoxy, unsubstituted thio(C₁-C₄ alkoxy), halo,hydroxy and dihydrogenphosphate substituents.
 16. A compound accordingto claim 1, wherein Y is hydrogen.
 17. A compound according to claim 1,wherein Ar is a substituted aryl or 5 to 10 membered heteroaryl groupwhich carries one substituent selected from a nitro or azido group and0, 1 or 2 further unsubstituted substituents chosen from halogen, C₁-C₆alkyl, hydroxy, amino, C₁-C₄ haloalkyl, C₁-C₄ alkoxy and C₁-C₄haloalkoxy substituents.
 18. A compound according to claim 1, wherein Aris an unsubstituted nitrophenyl, unsubstituted nitroimidazole,unsubstituted nitrothiophene or unsubstituted nitrofuranyl group.
 19. Acompound according to claim 1, wherein Ar is a group of formula (3),wherein R₉ is an unsubstituted C₁-C₆ alkyl group.
 20. A compoundaccording to claim 19, wherein R₉ is an unsubstituted C₁-C₂ alkyl group.21. A compound according to claim 1, wherein R₁₀ is selected fromhydrogen, unsubstituted C₁-C₆ alkyl, unsubstituted C₁-C₄ alkoxy andunsubstituted di(C₁-C₆ alkyl)amino(C₁-C₆ alkyl) substituents.
 22. Acompound according to claim 21, wherein R₁₀ is an unsubstituted C₁-C₂alkyl group.
 23. A compound according to claim 1, wherein R₁₁ and R₁₂are the same or different and each represent an unsubstitutedsubstituent selected from hydrogen, C₁-C₆ alkyl, C₁-C₄ alkoxy,thio(C₁-C₄ alkoxy), amino, (C₁-C₆ alkyl)amino, di(C₁-C₆ alkyl)amino,morpholino, (C₁-C₆ alkyl)morpholino, piperidino, (C₁-C₆alkyl)piperidino, piperazino, (C₁-C₆ alkyl)piperazino and 1-aziridinylsubstituents.
 24. A compound according to claim 23, wherein R₁₁ and R₁₂are the same or different and each represent a substituent selected fromhydrogen, unsubstituted C₁-C₂ alkoxy and unsubstituted (C₁-C₂alkyl)piperidino substituents.
 25. A compound according to claim 1 whichis 1-(4-methoxy-3-(5-nitrothien-2-yl)methoxy)phenyl-2-(3,4,5-trimethoxy)phenyl-Z-ethene,1-(4-Methoxy-3-(1-(5-nitrothien-2-yl)ethoxy))phenyl-2-(3,4,5-trimethoxy)phenyl-Z-ethene,1-(4-Methoxy-3-(5-nitrothien-2-yl)methoxycarbonyloxy)phenyl-2-(3,4,5-trimethoxy)phenyl-Z-ethene,5-Methoxy-3-((3,4,4′,5-tetramethoxy-(Z)-stilbene-3′-yl)oxy)methyl-1,2-dimethylindole-4,7-dioneor3-((3,4,4′,5-Tetramethoxy-(Z)-stilbene-3′-yl)oxy)methyl-1,2-dimethyl-5-(4-methylpiperazin-1-yl)indole-4,7-dione, or a pharmaceutically acceptable saltthereof.
 26. A pharmaceutical composition comprising a compoundaccording to claim 1, or a pharmaceutically acceptable salt thereof, anda pharmaceutically acceptable carrier or diluent.
 27. A method ofameliorating or reducing the incidence of a proliferative disorder in apatient, which method comprises administering to said patient aneffective amount of a compound as defined in claim 1, or apharmaceutically acceptable salt thereof.
 28. (canceled)
 29. A methodaccording to claim 27, wherein the proliferative disorder is cancer,rheumatoid arthritis, psoriatic lesions, diabetic retinopathy or wetage-related macular degeneration.
 30. A method according to claim 27,wherein the proliferative disorder is a hypoxic disorder.
 31. A methodaccording to claim 27, wherein the medicament is for use in theprevention or treatment of a solid tumour or leukaemia.
 32. (canceled)33. A method according to claim 30, which method comprises administeringto said patient an effective amount of: (a) a compound as defined inclaim 1, or a pharmaceutically acceptable salt thereof; and (b) areductase, an anti-body reductase conjugate, a macromolecule-reductaseconjugate or DNA encoding a reductase gene.
 34. (canceled)